CDMA (Code Division Multiple Access) is a technology for transmission channel access, which allows a simultaneous transmission of several signals within the same band of frequencies. CDMA is used in mobile communications and satellite transmissions, for example to transmit different payload data streams in the same frequency range from satellites of a Global Navigation Satellite System (GNSS) such as NAVSTAR-GPS or the planned European GNSS called GALILEO to users. CDMA is also used for terrestrial telecommunication networks, for example in mobile communication networks of the 3rd generation.
The term CDMA signal as used herein designates a code-modulated signal, i.e. a signal whose symbols are modulated with a spreading sequence or spreading code, which is transmitted from a sender such as a GNSS satellite to a receiver such as a GNSS positioning system. For example, in (NAVSTAR-) GPS to each satellite an unique C/A (coarse access) code and an unique P (precision) code are assigned as spreading codes for generating and transmitting CDMA signals. When several code-modulated signals are transmitted on the same carrier, the corresponding aggregate signal is called multiplexed or interplexed CDMA signal. Each elementary CDMA signal building the multiplexed CDMA signal is called a component.
Acquisition, tracking and data demodulation of multiplexed CDMA signals require sophisticated signal processing algorithms, which are able to extract the data contained in a received CDMA signal without a loss of information. A critical factor in CDMA systems is thermal noise, which is one of the main reasons for performance degradations. Thermal noise is usually incurred by the transmission channel and active elements of the receiver front-end.